With the explosion of INTERNET and multimedia applications, it is an increasing challenge to provide high-bandwidth, last-mile connectivity to end-users. Communications signals can be delivered to such users through a number of different types of communications systems. A wired, terrestrial system typically provides high speed communication for a large bandwidth signal. However, the infrastructure for such a system is expensive and time consuming to build, maintain and upgrade, and it does not, by itself, support mobile communications. A wireless system that uses transmission towers provides reasonably high speed communication for a substantially more limited bandwidth per the ground area served.
Geostationary Earth orbit (GEO) satellites (at an altitude of about 36,000 kilometers) can also provide wireless communications to end-users, but are limited by bandwidth efficiency, and therefore under serve highly populated areas. Medium and low Earth orbit (MEO and LEO) satellite (10,000 kilometers and 700-1500 kilometers, respectively) systems are complex in nature because end-user's are required to have equipment to track the satellites' relative movement. Furthermore, GEO satellites must be in equatorial orbits, which limits their practical use to equatorial land regions. Non-geostationary satellites require complex, continuously adjusting, directional antennas, both in the air and on the ground, typically with secondary systems adapted to switching communications signals from one passing satellite to the next. Of course, none of the above satellites are easily retrieved, e.g., for servicing.
Aircraft are used in a wide variety of applications, including travel, transportation, fire fighting, surveillance and combat. Various aircraft have been designed to fill the wide array of functional roles defined by these applications. Included among these aircraft are traditional balloons, dirigibles, fixed wing to airplanes, flying wing airplanes and helicopters.
One functional role that aircraft have not typically been designed to fill is that of a long duration, suborbital (e.g., stratospheric), high-altitude platform for communication. High altitude platforms are aircraft, stationed at high altitudes, that are relatively fixed in location. Lighter-than-air aircraft, such as balloons and dirigibles, and helicopters are both limited in their functionality as high altitude platforms by altitude limitations, and by an inability to maintain a selected station in strong winds. Airplanes, which typically travel at high speeds to reach and maintain high altitudes, are limited by an inability to maintain a selected station in calm winds. Furthermore, helicopters, some lighter-than-air aircraft, and most airplanes are unable to maintain a high-altitude station for much more than a day, let alone a significant length of time such as over a week or a month.
A number of developmental airplanes have the potential to sustain continuous day and night flight as solar-powered airplanes for as long as ample sunlight is available during the day. Three such airplanes that were actually constructed, being the well-known Pathfinder, Centurion and Helios airplanes, have set numerous flight records. The basic design underlying these airplanes is discussed at length in U.S. Pat. No. 5,810,284, which is directed toward an unswept flying wing airplane having a very high aspect ratio and a relatively constant chord and airfoil.
Long duration high altitude platforms that operate at suborbital altitudes, such as the Pathfinder, Centurion and Helios airplanes, have been suggested for use in a variety of functions. As one example, a high altitude platform equipped with microwave communications equipment could provide communication relay services between remote areas. Other types of airplanes are not optimally suited to this task because they are limited by the amount of combustible fuels that they use, which are heavy, expensive and are consumed very quickly. Typically, these other types of airplanes cannot remain over their desired location for any significant length of time, and hence, are of limited utility in performing these tasks.
It is desirable to develop a communications system that provides for high bandwidth signals to both fixed-location and mobile receivers. Various embodiments of the present invention can meet some or all of these needs, and provide further, related advantages.